The present invention relates to continuous manufacturing method and manufacturing apparatus of thermoplastic polyester resin foam. More particularly, it relates to continuous manufacturing method and manufacturing apparatus of foam characterized by reusing recovered material made of recycled thermoplastic polyester resin.
Thermoplastic polyester resin (hereinafter called PET) is engineering plastics excellent in heat resistance, chemical resistance and weather resistance, and also superior in tensile strength and other mechanical properties. This resin is mass produced by blow forming or the like and used widely as liquid containers. The PET is a crystalline resin, so that it is difficult to make resin foam, but it is extruded and foamed by adding a crosslinking agent as disclosed in the U.S. Pat. No. 5,000,991 to obtain a foamed sheet, and this foamed sheet is heated and formed into a container, and is recently used as a heat resistant container usable in heating and cooking in a microwave oven.
Such containers find no applications after the contained merchandise is consumed. The system for recycling a huge quantity of used containers has been regulated by law in various nations in relation to environmental problems. In this background there is a mounting need for effectively reusing the recycled containers.
Moreover, the PET has a moisture absorbing property, and when the resin containing moisture is put in an extruder heated to high temperature, it is hydrolyzed and deteriorates, and therefore it must be dried to 300 ppm or less. For example, in the specification of WO95/15257, the trimming loss of PET foamed sheet is ground and reused. This ground material is dried preliminarily. In this drying process, usually, the ground material is put in a dryer and is heated for some time while circulating dry air. The ground material of foam is bulky and a large dryer is needed, and the heating time must be kept for at least several hours, and hence this drying process is complicated, and omission of this drying has been expected. Besides, the dried state varies significantly, and it leads to fluctuations of the supply materials.
As disclosed in Japanese Patent Publication (TOKKYO KOKOKU) No. 60-54850, it has been known to fuse polystyrene resin, evacuate and suck from the barrel of an extruder to remove volatile components such as residual monomer, and inject foaming agent, thereby extruding and foaming. Incidentally, it was unexpected that PET foam of high quality free from deterioration of PET can be continuously extruded and foamed by applying this method in recycled PET, without drying process of PET, as the moisture is sufficiently removed by evacuation and suction in the extruder.
It is hence a primary object of the invention to present a continuous manufacturing method of high quality PET foam, by solving the conventional problems, and using the recovered material from a huge quantity of recycled PET containers.
It is other object of the invention to present a continuous manufacturing method of PET foam capable of feeding unfoamed or foamed ground material of recycled PET directly into an extruder.
It is another object of the invention to present an efficient continuous manufacturing method of PET foam capable of removing moisture only by evacuating and sucking from the barrel of an extruder, without complicated drying process of PET. It is a different object of the invention to present a continuous manufacturing method of foam being less in deterioration of PET in high temperature extrusion, by removing moisture by evacuating and sucking from the barrel of an extruder.
It is a further object of the invention to present a continuous manufacturing method of PET foam modified in PET deteriorated by addition of crosslinking agent, and improved in foaming property.
It is a further different object of the invention to present a continuous manufacturing apparatus of PET foam for executing the foregoing objects.
To achieve the above objects, the present inventor intensively researched and finally reached this invention.
That is, when fusing and kneading the PET in an extruder, although the PET is increased in its melt viscosity, only by evacuating and sucking from the barrel of the extruder, it was confirmed that the moisture can be sufficiently removed from the PET so as to avoid deterioration. The invention is based on such finding.
The invention therefore provides a continuous manufacturing method of thermoplastic polyester resin foam characterized by adding a crosslinking agent to a thermoplastic polyester resin, feeding into an extruder, fusing and kneading in the extruder to increase the weight-average molecular weight of the resin, evacuating and sucking from the barrel of the extruder to remove moisture from the fused resin, injecting a foaming agent into the fused resin to obtain a formed fused resin, and extruding and foaming it from the extruder into a low pressure region, and a manufacturing apparatus of thermoplastic polyester resin foam comprising an extruder having a vent port in the portion corresponding to the resin fusing section of the barrel, an extruder having a foaming agent pressure feed port on the way of the barrel, a connection tube for coupling these two extruders, an evacuating device consecutive to the vent port, and a die attached to the front end of the extruder.